Rach quasi-colocation association

ABSTRACT

In an aspect of the disclosure, a method, a computer-readable medium, and an apparatus are provided. The apparatus may be a UE. The UE determines that a random access event has occurred. The UE detects one or more down-link reference signals that are UE-specifically configured or predefined. The UE further selects a first message that is associated with a first down-link reference signal of the one or more down-link reference signals, the first down-link reference signal being quasi-colocated with a first DMRS of a serving control channel of the UE. The UE sends the first message to a base station to request a random access to the base station.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefits of U.S. Provisional Application Ser. No. 62/557,199, entitled “RACH PROCEDURE IN NR” and filed on Sep. 12, 2017, and U.S. Provisional Application Ser. No. 62/558,895, entitled “RACH PROCEDURE IN NR” and filed on Sep. 15, 2017, which are expressly incorporated by reference herein in their entirety.

BACKGROUND Field

The present disclosure relates generally to communication systems, and more particularly, to a random access procedure employed by a user equipment (UE).

Background

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasts. Typical wireless communication systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources. Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency division multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems.

These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example telecommunication standard is 5G New Radio (NR). 5G NR is part of a continuous mobile broadband evolution promulgated by Third Generation Partnership Project (3GPP) to meet new requirements associated with latency, reliability, security, scalability (e.g., with Internet of Things (IoT)), and other requirements. Some aspects of 5G NR may be based on the 4G Long Term Evolution (LTE) standard. There exists a need for further improvements in 5G NR technology. These improvements may also be applicable to other multi-access technologies and the telecommunication standards that employ these technologies.

SUMMARY

The following presents a simplified summary of one or more aspects in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements of all aspects nor delineate the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.

In an aspect of the disclosure, a method, a computer-readable medium, and an apparatus are provided. The apparatus may be a UE. The UE determines that a random access event has occurred. The UE detects one or more down-link reference signals that are UE-specifically configured or predefined. The UE further selects a first message that is associated with a first down-link reference signal of the one or more down-link reference signals, the first down-link reference signal being quasi-colocated with a first DMRS of a serving control channel of the UE. The UE sends the first message to a base station to request a random access to the base station.

To the accomplishment of the foregoing and related ends, the one or more aspects comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative features of the one or more aspects. These features are indicative, however, of but a few of the various ways in which the principles of various aspects may be employed, and this description is intended to include all such aspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a wireless communications system and an access network.

FIG. 2 is a diagram illustrating a base station in communication with a UE in an access network.

FIG. 3 illustrates an example logical architecture of a distributed access network.

FIG. 4 illustrates an example physical architecture of a distributed access network.

FIG. 5 is a diagram showing an example of a DL-centric subframe.

FIG. 6 is a diagram showing an example of an UL-centric subframe.

FIG. 7 is a diagram illustrating communications between a base station and UE.

FIG. 8 is a diagram illustrating a random access procedure of a UE in a connected state.

FIG. 9 is a flow chart of a method (process) for accessing a base station.

FIG. 10 is a conceptual data flow diagram illustrating the data flow between different components/means in an exemplary apparatus.

FIG. 11 is a diagram illustrating an example of a hardware implementation for an apparatus employing a processing system.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well known structures and components are shown in block diagram form in order to avoid obscuring such concepts.

Several aspects of telecommunication systems will now be presented with reference to various apparatus and methods. These apparatus and methods will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, components, circuits, processes, algorithms, etc. (collectively referred to as “elements”). These elements may be implemented using electronic hardware, computer software, or any combination thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.

By way of example, an element, or any portion of an element, or any combination of elements may be implemented as a “processing system” that includes one or more processors. Examples of processors include microprocessors, microcontrollers, graphics processing units (GPUs), central processing units (CPUs), application processors, digital signal processors (DSPs), reduced instruction set computing (RISC) processors, systems on a chip (SoC), baseband processors, field programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure. One or more processors in the processing system may execute software. Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software components, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise.

Accordingly, in one or more example embodiments, the functions described may be implemented in hardware, software, or any combination thereof. If implemented in software, the functions may be stored on or encoded as one or more instructions or code on a computer-readable medium. Computer-readable media includes computer storage media. Storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise a random-access memory (RAM), a read-only memory (ROM), an electrically erasable programmable ROM (EEPROM), optical disk storage, magnetic disk storage, other magnetic storage devices, combinations of the aforementioned types of computer-readable media, or any other medium that can be used to store computer executable code in the form of instructions or data structures that can be accessed by a computer.

FIG. 1 is a diagram illustrating an example of a wireless communications system and an access network 100. The wireless communications system (also referred to as a wireless wide area network (WWAN)) includes base stations 102, UEs 104, and an Evolved Packet Core (EPC) 160. The base stations 102 may include macro cells (high power cellular base station) and/or small cells (low power cellular base station). The macro cells include base stations. The small cells include femtocells, picocells, and microcells.

The base stations 102 (collectively referred to as Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN)) interface with the EPC 160 through backhaul links 132 (e.g., S1 interface). In addition to other functions, the base stations 102 may perform one or more of the following functions: transfer of user data, radio channel ciphering and deciphering, integrity protection, header compression, mobility control functions (e.g., handover, dual connectivity), inter-cell interference coordination, connection setup and release, load balancing, distribution for non-access stratum (NAS) messages, NAS node selection, synchronization, radio access network (RAN) sharing, multimedia broadcast multicast service (MBMS), subscriber and equipment trace, RAN information management (RIM), paging, positioning, and delivery of warning messages. The base stations 102 may communicate directly or indirectly (e.g., through the EPC 160) with each other over backhaul links 134 (e.g., X2 interface). The backhaul links 134 may be wired or wireless.

The base stations 102 may wirelessly communicate with the UEs 104. Each of the base stations 102 may provide communication coverage for a respective geographic coverage area 110. There may be overlapping geographic coverage areas 1 10. For example, the small cell 102′ may have a coverage area 110′ that overlaps the coverage area 110 of one or more macro base stations 102. A network that includes both small cell and macro cells may be known as a heterogeneous network. A heterogeneous network may also include Home Evolved Node Bs (eNBs) (HeNBs), which may provide service to a restricted group known as a closed subscriber group (CSG). The communication links 120 between the base stations 102 and the UEs 104 may include uplink (UL) (also referred to as reverse link) transmissions from a UE 104 to a base station 102 and/or downlink (DL) (also referred to as forward link) transmissions from a base station 102 to a UE 104. The communication links 120 may use multiple-input and multiple-output (MIMO) antenna technology, including spatial multiplexing, beamforming, and/or transmit diversity. The communication links may be through one or more carriers. The base stations 102/UEs 104 may use spectrum up to Y MHz (e.g., 5, 10, 15, 20, 100 MHz) bandwidth per carrier allocated in a carrier aggregation of up to a total of Yx MHz (x component carriers) used for transmission in each direction. The carriers may or may not be adjacent to each other. Allocation of carriers may be asymmetric with respect to DL and UL (e.g., more or less carriers may be allocated for DL than for UL). The component carriers may include a primary component carrier and one or more secondary component carriers. A primary component carrier may be referred to as a primary cell (PCell) and a secondary component carrier may be referred to as a secondary cell (SCell).

The wireless communications system may further include a Wi-Fi access point (AP) 150 in communication with Wi-Fi stations (STAs) 152 via communication links 154 in a 5 GHz unlicensed frequency spectrum. When communicating in an unlicensed frequency spectrum, the STAs 152/AP 150 may perform a clear channel assessment (CCA) prior to communicating in order to determine whether the channel is available.

The small cell 102′ may operate in a licensed and/or an unlicensed frequency spectrum. When operating in an unlicensed frequency spectrum, the small cell 102′ may employ NR and use the same 5 GHz unlicensed frequency spectrum as used by the Wi-Fi AP 150. The small cell 102′, employing NR in an unlicensed frequency spectrum, may boost coverage to and/or increase capacity of the access network.

The gNodeB (gNB) 180 may operate in millimeter wave (mmW) frequencies and/or near mmW frequencies in communication with the UE 104. When the gNB 180 operates in mmW or near mmW frequencies, the gNB 180 may be referred to as an mmW base station. Extremely high frequency (EHF) is part of the RF in the electromagnetic spectrum. EHF has a range of 30 GHz to 300 GHz and a wavelength between 1 millimeter and 10 millimeters. Radio waves in the band may be referred to as a millimeter wave. Near mmW may extend down to a frequency of 3 GHz with a wavelength of 100 millimeters. The super high frequency (SHF) band extends between 3 GHz and 30 GHz, also referred to as centimeter wave. Communications using the mmW/near mmW radio frequency band has extremely high path loss and a short range. The mmW base station 180 may utilize beamforming 184 with the UE 104 to compensate for the extremely high path loss and short range.

The EPC 160 may include a Mobility Management Entity (MME) 162, other MMEs 164, a Serving Gateway 166, a Multimedia Broadcast Multicast Service (MBMS) Gateway 168, a Broadcast Multicast Service Center (BM-SC) 170, and a Packet Data Network (PDN) Gateway 172. The MME 162 may be in communication with a Home Subscriber Server (HSS) 174. The MME 162 is the control node that processes the signaling between the UEs 104 and the EPC 160. Generally, the MME 162 provides bearer and connection management. All user Internet protocol (IP) packets are transferred through the Serving Gateway 166, which itself is connected to the PDN Gateway 172. The PDN Gateway 172 provides UE IP address allocation as well as other functions. The PDN Gateway 172 and the BM-SC 170 are connected to the IP Services 176. The IP Services 176 may include the Internet, an intranet, an IP Multimedia Subsystem (IMS), a PS Streaming Service (PSS), and/or other IP services. The BM-SC 170 may provide functions for MBMS user service provisioning and delivery. The BM-SC 170 may serve as an entry point for content provider MBMS transmission, may be used to authorize and initiate MBMS Bearer Services within a public land mobile network (PLMN), and may be used to schedule MBMS transmissions. The MBMS Gateway 168 may be used to distribute MBMS traffic to the base stations 102 belonging to a Multicast Broadcast Single Frequency Network (MBSFN) area broadcasting a particular service, and may be responsible for session management (start/stop) and for collecting eMBMS related charging information.

The base station may also be referred to as a gNB, Node B, evolved Node B (eNB), an access point, a base transceiver station, a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS), an extended service set (ESS), or some other suitable terminology. The base station 102 provides an access point to the EPC 160 for a UE 104. Examples of UEs 104 include a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a personal digital assistant (PDA), a satellite radio, a global positioning system, a multimedia device, a video device, a digital audio player (e.g., MP3 player), a camera, a game console, a tablet, a smart device, a wearable device, a vehicle, an electric meter, a gas pump, a toaster, or any other similar functioning device. Some of the UEs 104 may be referred to as IoT devices (e.g., parking meter, gas pump, toaster, vehicles, etc.). The UE 104 may also be referred to as a station, a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a mobile client, a client, or some other suitable terminology.

In certain aspects, the UE 104 includes, among other components, an event component 192, a detection component 194, and a random access component 198. The event component 192 determining that a random access event has occurred. The detection component 194 detects one or more down-link reference signals that are UE-specifically configured or predefined. The random access component 198 selects a first message that is associated with a first down-link reference signal of the one or more down-link reference signals, the first down-link reference signal being quasi-colocated with a first Demodulation Reference Signal (DMRS) of a serving control channel of the UE. The UE 104 sends the first message to a base station to request a random access to the base station.

FIG. 2 is a block diagram of a base station 210 in communication with a UE 250 in an access network. In the DL, IP packets from the EPC 160 may be provided to a controller/processor 275. The controller/processor 275 implements layer 3 and layer 2 functionality. Layer 3 includes a radio resource control (RRC) layer, and layer 2 includes a packet data convergence protocol (PDCP) layer, a radio link control (RLC) layer, and a medium access control (MAC) layer. The controller/processor 275 provides RRC layer functionality associated with broadcasting of system information (e.g., MIB, SIBs), RRC connection control (e.g., RRC connection paging, RRC connection establishment, RRC connection modification, and RRC connection release), inter radio access technology (RAT) mobility, and measurement configuration for UE measurement reporting; PDCP layer functionality associated with header compression/decompression, security (ciphering, deciphering, integrity protection, integrity verification), and handover support functions; RLC layer functionality associated with the transfer of upper layer packet data units (PDUs), error correction through ARQ, concatenation, segmentation, and reassembly of RLC service data units (SDUs), re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functionality associated with mapping between logical channels and transport channels, multiplexing of MAC SDUs onto transport blocks (TBs), demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction through HARQ, priority handling, and logical channel prioritization.

The transmit (TX) processor 216 and the receive (RX) processor 270 implement layer 1 functionality associated with various signal processing functions. Layer 1, which includes a physical (PHY) layer, may include error detection on the transport channels, forward error correction (FEC) coding/decoding of the transport channels, interleaving, rate matching, mapping onto physical channels, modulation/demodulation of physical channels, and MIMO antenna processing. The TX processor 216 handles mapping to signal constellations based on various modulation schemes (e.g., binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), M-phase-shift keying (M-PSK), M-quadrature amplitude modulation (M-QAM)). The coded and modulated symbols may then be split into parallel streams. Each stream may then be mapped to an OFDM subcarrier, multiplexed with a reference signal (e.g., pilot) in the time and/or frequency domain, and then combined together using an Inverse Fast Fourier Transform (IFFT) to produce a physical channel carrying a time domain OFDM symbol stream. The OFDM stream is spatially precoded to produce multiple spatial streams. Channel estimates from a channel estimator 274 may be used to determine the coding and modulation scheme, as well as for spatial processing. The channel estimate may be derived from a reference signal and/or channel condition feedback transmitted by the UE 250. Each spatial stream may then be provided to a different antenna 220 via a separate transmitter 218TX. Each transmitter 218TX may modulate an RF carrier with a respective spatial stream for transmission.

At the UE 250, each receiver 254RX receives a signal through its respective antenna 252. Each receiver 254RX recovers information modulated onto an RF carrier and provides the information to the receive (RX) processor 256. The TX processor 268 and the RX processor 256 implement layer 1 functionality associated with various signal processing functions. The RX processor 256 may perform spatial processing on the information to recover any spatial streams destined for the UE 250. If multiple spatial streams are destined for the UE 250, they may be combined by the RX processor 256 into a single OFDM symbol stream. The RX processor 256 then converts the OFDM symbol stream from the time-domain to the frequency domain using a Fast Fourier Transform (FFT). The frequency domain signal comprises a separate OFDM symbol stream for each subcarrier of the OFDM signal. The symbols on each subcarrier, and the reference signal, are recovered and demodulated by determining the most likely signal constellation points transmitted by the base station 210. These soft decisions may be based on channel estimates computed by the channel estimator 258. The soft decisions are then decoded and deinterleaved to recover the data and control signals that were originally transmitted by the base station 210 on the physical channel. The data and control signals are then provided to the controller/processor 259, which implements layer 3 and layer 2 functionality.

The controller/processor 259 can be associated with a memory 260 that stores program codes and data. The memory 260 may be referred to as a computer-readable medium. In the UL, the controller/processor 259 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, and control signal processing to recover IP packets from the EPC 160. The controller/processor 259 is also responsible for error detection using an ACK and/or NACK protocol to support HARQ operations.

Similar to the functionality described in connection with the DL transmission by the base station 210, the controller/processor 259 provides RRC layer functionality associated with system information (e.g., MIB, SIBs) acquisition, RRC connections, and measurement reporting; PDCP layer functionality associated with header compression/decompression, and security (ciphering, deciphering, integrity protection, integrity verification); RLC layer functionality associated with the transfer of upper layer PDUs, error correction through ARQ, concatenation, segmentation, and reassembly of RLC SDUs, re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functionality associated with mapping between logical channels and transport channels, multiplexing of MAC SDUs onto TBs, demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction through HARQ, priority handling, and logical channel prioritization.

Channel estimates derived by a channel estimator 258 from a reference signal or feedback transmitted by the base station 210 may be used by the TX processor 268 to select the appropriate coding and modulation schemes, and to facilitate spatial processing. The spatial streams generated by the TX processor 268 may be provided to different antenna 252 via separate transmitters 254TX. Each transmitter 254TX may modulate an RF carrier with a respective spatial stream for transmission. The UL transmission is processed at the base station 210 in a manner similar to that described in connection with the receiver function at the UE 250. Each receiver 218RX receives a signal through its respective antenna 220. Each receiver 218RX recovers information modulated onto an RF carrier and provides the information to a RX processor 270.

The controller/processor 275 can be associated with a memory 276 that stores program codes and data. The memory 276 may be referred to as a computer-readable medium. In the UL, the controller/processor 275 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover IP packets from the UE 250. IP packets from the controller/processor 275 may be provided to the EPC 160. The controller/processor 275 is also responsible for error detection using an ACK and/or NACK protocol to support HARQ operations.

New radio (NR) may refer to radios configured to operate according to a new air interface (e.g., other than Orthogonal Frequency Divisional Multiple Access (OFDMA)-based air interfaces) or fixed transport layer (e.g., other than Internet Protocol (IP)). NR may utilize OFDM with a cyclic prefix (CP) on the uplink and downlink and may include support for half-duplex operation using time division duplexing (TDD). NR may include Enhanced Mobile Broadband (eMBB) service targeting wide bandwidth (e.g. 80 MHz beyond), millimeter wave (mmW) targeting high carrier frequency (e.g. 60 GHz), massive MTC (mMTC) targeting non-backward compatible MTC techniques, and/or mission critical targeting ultra-reliable low latency communications (URLLC) service.

A single component carrier bandwidth of 100 MHZ may be supported. In one example, NR resource blocks (RBs) may span 12 sub-carriers with a sub-carrier bandwidth of 60 kHz over a 0.125 ms duration or a bandwidth of 15 kHz over a 0.5 ms duration. Each radio frame may consist of 20 or 80 subframes (or NR slots) with a length of 10 ms. Each subframe may indicate a link direction (i.e., DL or UL) for data transmission and the link direction for each subframe may be dynamically switched. Each subframe may include DL/UL data as well as DL/UL control data. UL and DL subframes for NR may be as described in more detail below with respect to FIGS. 5 and 6.

The NR RAN may include a central unit (CU) and distributed units (DUs). A NR BS (e.g., gNB, 5G Node B, Node B, transmission reception point (TRP), access point (AP)) may correspond to one or multiple BSs. NR cells can be configured as access cells (ACells) or data only cells (DCells). For example, the RAN (e.g., a central unit or distributed unit) can configure the cells. DCells may be cells used for carrier aggregation or dual connectivity and may not be used for initial access, cell selection/reselection, or handover. In some cases DCells may not transmit synchronization signals (SS) in some cases DCells may transmit SS. NR BSs may transmit downlink signals to UEs indicating the cell type. Based on the cell type indication, the UE may communicate with the NR BS. For example, the UE may determine NR BSs to consider for cell selection, access, handover, and/or measurement based on the indicated cell type.

FIG. 3 illustrates an example logical architecture 300 of a distributed RAN, according to aspects of the present disclosure. A 5G access node 306 may include an access node controller (ANC) 302. The ANC may be a central unit (CU) of the distributed RAN 300. The backhaul interface to the next generation core network (NG-CN) 304 may terminate at the ANC. The backhaul interface to neighboring next generation access nodes (NG-ANs) may terminate at the ANC. The ANC may include one or more TRPs 308 (which may also be referred to as BSs, NR BSs, Node Bs, 5G NBs, APs, or some other term). As described above, a TRP may be used interchangeably with “cell.”

The TRPs 308 may be a distributed unit (DU). The TRPs may be connected to one ANC (ANC 302) or more than one ANC (not illustrated). For example, for RAN sharing, radio as a service (RaaS), and service specific AND deployments, the TRP may be connected to more than one ANC. A TRP may include one or more antenna ports. The TRPs may be configured to individually (e.g., dynamic selection) or jointly (e.g., joint transmission) serve traffic to a UE.

The local architecture of the distributed RAN 300 may be used to illustrate fronthaul definition. The architecture may be defined that support fronthauling solutions across different deployment types. For example, the architecture may be based on transmit network capabilities (e.g., bandwidth, latency, and/or jitter). The architecture may share features and/or components with LTE. According to aspects, the next generation AN (NG-AN) 310 may support dual connectivity with NR. The NG-AN may share a common fronthaul for LTE and NR.

The architecture may enable cooperation between and among TRPs 308. For example, cooperation may be preset within a TRP and/or across TRPs via the ANC 302. According to aspects, no inter-TRP interface may be needed/present.

According to aspects, a dynamic configuration of split logical functions may be present within the architecture of the distributed RAN 300. The PDCP, RLC, MAC protocol may be adaptably placed at the ANC or TRP.

FIG. 4 illustrates an example physical architecture of a distributed RAN 400, according to aspects of the present disclosure. A centralized core network unit (C-CU) 402 may host core network functions. The C-CU may be centrally deployed. C-CU functionality may be offloaded (e.g., to advanced wireless services (AWS)), in an effort to handle peak capacity. A centralized RAN unit (C-RU) 404 may host one or more ANC functions. Optionally, the C-RU may host core network functions locally. The C-RU may have distributed deployment. The C-RU may be closer to the network edge. A distributed unit (DU) 406 may host one or more TRPs. The DU may be located at edges of the network with radio frequency (RF) functionality.

FIG. 5 is a diagram 500 showing an example of a DL-centric subframe. The DL-centric subframe may include a control portion 502. The control portion 502 may exist in the initial or beginning portion of the DL-centric subframe. The control portion 502 may include various scheduling information and/or control information corresponding to various portions of the DL-centric subframe. In some configurations, the control portion 502 may be a physical DL control channel (PDCCH), as indicated in FIG. 5. The DL-centric subframe may also include a DL data portion 504. The DL data portion 504 may sometimes be referred to as the payload of the DL-centric subframe. The DL data portion 504 may include the communication resources utilized to communicate DL data from the scheduling entity (e.g., UE or BS) to the subordinate entity (e.g., UE). In some configurations, the DL data portion 504 may be a physical DL shared channel (PDSCH).

The DL-centric subframe may also include a common UL portion 506. The common UL portion 506 may sometimes be referred to as an UL burst, a common UL burst, and/or various other suitable terms. The common UL portion 506 may include feedback information corresponding to various other portions of the DL-centric subframe. For example, the common UL portion 506 may include feedback information corresponding to the control portion 502. Non-limiting examples of feedback information may include an ACK signal, a NACK signal, a HARQ indicator, and/or various other suitable types of information. The common UL portion 506 may include additional or alternative information, such as information pertaining to random access channel (RACH) procedures, scheduling requests (SRs), and various other suitable types of information.

As illustrated in FIG. 5, the end of the DL data portion 504 may be separated in time from the beginning of the common UL portion 506. This time separation may sometimes be referred to as a gap, a guard period, a guard interval, and/or various other suitable terms. This separation provides time for the switch-over from DL communication (e.g., reception operation by the subordinate entity (e.g., UE)) to UL communication (e.g., transmission by the subordinate entity (e.g., UE)). One of ordinary skill in the art will understand that the foregoing is merely one example of a DL-centric subframe and alternative structures having similar features may exist without necessarily deviating from the aspects described herein.

FIG. 6 is a diagram 600 showing an example of an UL-centric subframe. The UL-centric subframe may include a control portion 602. The control portion 602 may exist in the initial or beginning portion of the UL-centric subframe. The control portion 602 in FIG. 6 may be similar to the control portion 502 described above with reference to FIG. 5. The UL-centric subframe may also include an UL data portion 604. The UL data portion 604 may sometimes be referred to as the pay load of the UL-centric subframe. The UL portion may refer to the communication resources utilized to communicate UL data from the subordinate entity (e.g., UE) to the scheduling entity (e.g., UE or BS). In some configurations, the control portion 602 may be a physical DL control channel (PDCCH).

As illustrated in FIG. 6, the end of the control portion 602 may be separated in time from the beginning of the UL data portion 604. This time separation may sometimes be referred to as a gap, guard period, guard interval, and/or various other suitable terms. This separation provides time for the switch-over from DL communication (e.g., reception operation by the scheduling entity) to UL communication (e.g., transmission by the scheduling entity). The UL-centric subframe may also include a common UL portion 606. The common UL portion 606 in FIG. 6 may be similar to the common UL portion 606 described above with reference to FIG. 6. The common UL portion 606 may additionally or alternatively include information pertaining to channel quality indicator (CQI), sounding reference signals (SRSs), and various other suitable types of information. One of ordinary skill in the art will understand that the foregoing is merely one example of an UL-centric subframe and alternative structures having similar features may exist without necessarily deviating from the aspects described herein.

In some circumstances, two or more subordinate entities (e.g., UEs) may communicate with each other using sidelink signals. Real-world applications of such sidelink communications may include public safety, proximity services, UE-to-network relaying, vehicle-to-vehicle (V2V) communications, Internet of Everything (IoE) communications, IoT communications, mission-critical mesh, and/or various other suitable applications. Generally, a sidelink signal may refer to a signal communicated from one subordinate entity (e.g., UE1) to another subordinate entity (e.g., UE2) without relaying that communication through the scheduling entity (e.g., UE or BS), even though the scheduling entity may be utilized for scheduling and/or control purposes. In some examples, the sidelink signals may be communicated using a licensed spectrum (unlike wireless local area networks, which typically use an unlicensed spectrum).

FIG. 7 is a diagram 700 illustrating communications between a base station 704 and a UE 702. The base station 704 may operates antenna ports 722-1 to 722-N. The base station 704 provides transmitter side beams 726-1 to 726-N at different directions. The UE 702 may use a random access procedure to gain access to a cell of the base station 704. In this example, to facilitate a UE to perform the random access procedure, the base station 704 transmits a set of synchronization signal blocks (SSBs) including SSBs 732-1 to 732-N, which are associated with the transmitter side beams 726-1 to 726-N, respectively. More specifically, the Primary Synchronization Signal (PSS) and the Secondary Synchronization Signal (SSS), together with the Physical Broadcast Channel (PBCH), are jointly referred to as an SSB. Each of the SSBs 732-1 to 732-N may include one or more Demodulation Reference Signals (DMRSs) for PBCH. The DMRSs are intended for channel estimation at a UE as part of coherent demodulation.

In certain configurations, the UE 702 may select one of the transmitter side beams 726-1 to 726-N randomly or based on a rule for deriving a corresponding preamble sequence used in the random access procedure. In certain configurations, the UE 702 may adjust the direction of a receiver side beam 728 to detect and measure the SSBs 732-1 to 732-N. Based on the detection and/or measurements (e.g., SNR measurements), the UE 702 may select a direction of the receiver side beam 728 and one of the transmitter side beams 726-1 to 726-N for deriving a corresponding preamble sequence used in the random access procedure.

In one example, the UE 702 may select the transmitter side beam 726-2 for deriving an associated preamble sequence for use in the random access procedure. More specifically, the UE 702 is configured with one or more preamble sequences associated with each particular one of the transmitter side beams 726-1 to 726-N. Accordingly, the UE 702 may select a preamble sequence 752 associated with the down-link reference signal of the transmitter side beam 726-2 (i.e., the selected one of the transmitter side beams 726-1 to 726-N). Subsequently, the UE 702 sends the preamble sequence 752 to the base station 704 through the receiver side beam 728 (by assuming a corresponding UE transmit beam can be derived from the receiver side beam 828). Base on the preamble sequence 752, the base station 704 can determine the transmitter side beam selected by the UE 702. Subsequently, the base station 704 and the UE 702 can further complete the random access procedure such that the base station 704 and the UE 702 can communicate through the transmitter side beam 726-2 and the receiver side beam 728. As such, the UE 702 is in a connected state (e.g., RRC CONNECTED) with the base station 704. The base station 704 may transmit CSI-RS sets 734-1 to 734-N that are specific to the UE 702 by using the transmitter side beams 726-1 to 726-N, respectively. A CSI-RS is used by the UE to estimate the channel and report channel state information (CSI) to the base station. A CSI-RS is configured on a per-device basis. The base station 704 may use the transmitter side beam 726-2 to transmit to the UE 702 a PDCCH 742, a PDSCH 744, and associated DMRSs 746.

FIG. 8 is diagram 800 illustrating a random access procedure of a UE in a connected state. In certain circumstances, the UE 702, although in a connected state, may need to conduct the random access procedure with the base station 704 or another base station. In this example, as described supra referring to FIG. 7, the UE 702 is connected to the base station 704. The UE 702 may receive a request (e.g., a PDCCH order) from the base station 704 to initiate a random access procedure again. The UE 702 may detect an up-link data arrival without up-link synchronization and, thus, may conduct the random access procedure with the base station 704. The UE 702 may detect a down-link data arrival without up-link synchronization and, thus, may conduct the random access procedure with the base station 704 and, thus, may conduct the random access procedure with the base station 704. The UE 702 may decide to recover a beam and, thus, may conduct the random access procedure with the base station 704. The UE 702 may be handed over from the base station 704 to another base station and, thus, may conduct the random access procedure with the other base station.

In this example, at procedure 802, the base station 704 sends a PDCCH order to the UE 702. In particular, the PDCCH order may be transmitted by using the transmitter side beam 726-2. Accordingly, upon received the PDCCH order, at procedure 803, the UE 702 initiates a random access procedure while in a connected state. In another example, the UE 702 may detect a beam failure and internally generates a beam failure recovery request. In response, the UE 702 can also initiate a random access procedure while in a connected state. At procedure 804, as described supra, the base station 704 sends the SSBs 732-1 to 732-N associated with the transmitter side beams 726-1 to 726-N, respectively. The UE 702 may detect some or all of the SSBs 732-1 to 732-N. Note that procedure 804 can also take place before procedure procedure 802.

In a first technique, at procedure 806, as described supra, in certain configurations, the UE 702 may select one of the transmitter side beams 726-1 to 726-N randomly or based on the measurement result. As an example, the base station 704 may select the transmitter side beam 726-1 for deriving an associated preamble sequence 752 for use in the random access procedure.

Accordingly, the base station 704 may use a correspondent beam of the transmitter side beam 726-1 to receive the preamble sequence 752, which is associated with the down-link reference signals of the transmitter side beam 726-1. The UE 702 determines a timing advance (TA) for the UE 702 based on the preamble sequence 752 received through the transmitter side beam 726-1.

In a second technique, at procedure 806, in certain configurations, after receiving the SSBs 732-1 to 732-N in procedure 804, the UE 702 may be configured to select a preamble sequence that is associated with a DL reference signal (e.g., SS block or CSI-RS) with which the DMRSs of the serving beam of the UE 702 (e.g., the DMRSs 746 on the transmitter side beam 726-2) are quasi-colocated through a one-level relationship or a multi-level relationship. More specifically, when there is only one-level of quasi-colocation relationship, in this example, the DMRSs 746 (and the antenna port 722-2) of the serving beam (e.g., the transmitter side beam 726-2) are directly quasi-colocated with the DL reference signal (e.g., the SSB 732-2, the CSI-RS set 734-2). When there are two levels (or more) of quasi-colocation relationships, the DMRSs 746 (and the antenna port 722-2) of the serving beam (e.g., the transmitter side beam 726-2) are quasi-colocated with the DL reference signals (e.g., the SSB 732-2, the CSI-RS set 734-2) via another quasi-colocation relationship with another set of down-link reference signals.

Accordingly, in the second technique, the UE 702 selects a down-link reference signal that is in a quasi-colocation relationship with the DMRSs 746 as the base for preamble sequence selection. In this example, the UE 702 selects the SSB 732-2 and/or the CSI-RS set 734-2 on the transmitter side beam 726-2, as the transmitter side beam 726-2 is the serving beam.

For the down-link reference signal selected by the UE 702 at procedure 806, the UE 702 may be configured with multiple preamble sequences associated with that down-link reference signal. Further, the UE 702 may receive from the base station 704 indications that some of the multiple preamble sequences are reserved for the UE 702. In this example, the UE 702 selects the SSB 732-2 and/or the CSI-RS set 734-2, as they are quasi-colocated with the DMRSs 746 on the transmitter side beam 726-2. The UE 702 selects a particular preamble sequence 752 from a group of preamble sequences associated with the the SSB 732-2 and/or the CSI-RS set 734-2. At procedure 808, the UE 702 transmits the preamble sequence 752 to the base station 704.

The base station 704 may receive the preamble sequence 752 on the transmitter side beam 726-2. The network of the base station 704 can also determine that the preamble sequence 752 is associated with the SSB 732-2 and/or the CSI-RS set 734-2 of the transmitter side beam 726-2. As such, the network learns that the UE 702 selected the transmitter side beam 726-2. At procedure 810, the base station 704 (under the control of the network) generates a random-access response (RAR). The RAR may include information about the preamble sequence 752 the network detected and for which the response is valid, a TA calculated by the network based on the preamble sequence receive timing, a scheduling grant indicating resources the UE 702 will use for the transmission of the subsequent message, and/or a temporary identity, the TC-RNTI, used for further communication between the device and the network.

At procedure 812, the base station 704 transmits a PDCCH scheduling command for scheduling transmission of the RAR by using the transmitter side beam 726-2. Accordingly, DMRS of the PDCCH scheduling command and DMRS of the PDCCH order at procedure 802 are quasi-colocated. Further, the PDCCH scheduling command may be scrambled by a cell radio network temporary identifier (C-RNTI) of the UE 702, which is known to the network.

At procedure 814, the base station 704 transmits the RAR to the UE 702 on the transmitter side beam 726-2. The RAR may be transmitted in a conventional downlink PDSCH. As such, the random access procedure completes for the UE 702, which is in a connected state.

In the example described supra referring to FIG. 8, the base station 704 knows the identity of the UE 702 and its C-RNTI. Further, the base station 704 reserves certain preamble sequences for the UE 702 to use. Therefore, no other UEs will be using those preamble sequences in the same set of resource blocks. Such a random access procedure is a non-contention based random access procedure.

In certain configurations, as described supra, in a non-contention based random access procedure, once the network identifies the UE 702 requesting the random access based on the reserved preamble sequence, the base station 704 can use the C-RNTI of the UE 702 to scramble the PDCCH command at procedure 812. In particular, C-RNTI can be used when the random access procedure is triggered by a beam failure recovery request. In certain configurations, for non-contention based random access procedure, the base station 704 can alternatively use an RA-RNTI to scramble the PDCCH command. Further, the base station 704 also use an RA-RNTI, which can be derived by the base station 704 based one or more techniques described infra, to scramble the PDCCH command in a contention based random access procedure.

In one technique, the RA-RNTI for the UE 702 can be derived from a set of variables that indicate the time/frequency resources used for the physical RACH preamble sequence. For example, the RA-RNTI can be derived from the starting symbol number of the preamble sequence 752 within a given time duration, the slot number of the preamble sequence 752 within a given time duration, the subframe number of the preamble sequence 752 within a given time duration, the index of a RACH time-frequency resource in the time dimension within a given time duration, and/or the index of RACH time-frequency resources in the frequency dimension within a time unit.

In particular, the index of the RACH time-frequency resource in the time dimension within a given time duration can be counted based on the actually allocated time-frequency resources under a given RACH configuration. Alternatively, the index of the RACH time-frequency resource can be counted based on the all RACH time-frequency resources that are possibly allocated under all RACH configuration. In addition, possible dynamically allocated RACH time-frequency resource can be taken into account. The given time duration may be a 10 ms radio frame, 5 ms (i.e. a half radio frame), the duration of a RACH burst set, and the periodicity of RACH burst sets

Further, RA-RNTI can be calculated based on the indices of RACH preamble sequences/time-frequency resources that are actually allocated under a RACH configuration. In addition, possible dynamically allocated RACH time-frequency resources can be taken into account in advance regarding RA-RNTI derivation.

RA-RNTI can be offset by a value that is a constant predefined in the specification. RA-RNTI can be offset by a value that is configurable by the network if specified by PDCCH signaling or high-layer signaling.

For dynamically allocated RACH transmission occasions (RACH time-frequency resources), the associated RA-RNTIs can be derived in a similar way as the semistatically allocated RACH resources. The associated RA-RNTIs can be fully or partially configured by the network. For example, a common starting value can be configured by the network.

The number of required RA-RNTI values can be reduced by allocating partial information of the detected preamble sequence to RAR. In other words, RAR can carry information of the detected preamble sequence that is not carried by RA-RNTI. Further, the number of required RA-RNTI values can be reduced by reducing the range of the given time duration to be less than a radio frame which may be 10 ms. The number of required RA-RNTI values can be reduced by restricting the possible allocated locations of RACH time-frequency resources in the time dimension especially when multibeam operations are considered. For example, not all every symbols or every slots are available to transmit PRACH. In this case, the time index is counted in a relative sense within the restricted possible locations.

In yet another technique, the RA-RNTI can be a function of RACH transmission occasion index within a given time duration (e.g., a 10 ms radio frame). A RACH transmission occasion is defined as the time-frequency resource on which a configured PRACH preamble sequence is transmitted on a single particular transmission beam. For example, in a 10 ms, a RACH transmission occasion may be available every 2 ms. Thus, in the 10 ms time period, there are 5 RACH transmission occasions.

Further, the RA-RNTI can be a function of the index of SS block. The index may be the absolute SS block index in an SSB burst set, or a relative index of SS block that have the same CORSESET configurations for carrying RAR.

The RA-RNTI can also be a function of the index of the corresponding SS block/CSIRS configuration.

The RA-RNTI can be a function of an index of CSIRS. The index may be an absolute CSIRS index with all CSIRS for the same purpose, or an relative index of CSIRS that have the same CORSESET configurations for their RA.

As described supra, the network may need to indicate, in the RAR, the particular preamble sequence received at the base station 704 and the RACH time-frequency resource (or RACH transmission occasion) on which the preamble sequence is transmitted. The RAR window, which is a time duration that UE is asked to monitor RAR, can be used to indicate the preamble sequence index. If RAR windows associated preamble sequences transmitted on different RACH transmission occasions are nonoverlapping, then RAR windows can be used to indicate the particular preamble sequence.

A CORESET is a time-frequency resource that is used to transmit PDCCH signals in NR. A CORESET can be used to indicate the preamble sequence index.

FIG. 9 is a flow chart 900 of a method (process) for accessing a base station. The method may be performed by a UE (e.g., the UE 702, the apparatus 1002, and the apparatus 1002′). At operation 902, the UE determines that a random access event has occurred. When the UE is in a connected state, the random access event includes at least one of: reception of a request from a base station (e.g., the base station 704) to initiate a random access to the base station, a handover of the UE from a second base station to the base station, an up-link data arrival without up-link synchronization, a down-link data arrival without up-link synchronization, and a beam recovery request.

At operation 904, the UE detects one or more down-link reference signals (e.g., the SSB 732-2, the CSI-RS set 734-2) that are UE-specifically configured or predefined. At operation 906, the UE selects a first message (e.g., the preamble sequence 752) that is associated with a first down-link reference signal (e.g., the SSB 732-2) of the one or more down-link reference signals. The first down-link reference signal is quasi-colocated with a first DMRS (e.g., the DMRSs 746) of a serving control channel (e.g., the transmitter side beam 726-2) of the UE. In certain configurations, the first message includes a preamble sequence. The first message is selected from a group of messages that are associated with the first down-link reference signal. In certain configurations, the first down-link reference signal is a channel state information reference signal (e.g., the CSI-RS set 734-2) or a synchronization signal block (e.g., the SSB 732-2) received. In certain configurations, the first down-link reference signal is directly quasi-colocated with the first DMRS. In certain configurations, the first down-link reference signal is quasi-colocated with the first DMRS through one or more intermediate signals.

At operation 908, the UE sends the first message to the base station to request a random access to the base station. At operation 910, the UE receives a second message from the base station in response to the first message. At operation 912, the UE assumes that a DMRS included in the request and a DMRS included in the second message are quasi-colocated for receiving the second message. In certain configurations, the request is a PDCCH order. The second message includes a PDCCH command and a random access response. In certain configurations, the random access event is the beam failure recovery request. The PDCCH command is scrambled by a C-RNTI of the UE.

FIG. 10 is a conceptual data flow diagram 1000 illustrating the data flow between different components/means in an exemplary apparatus 1002. The apparatus 1002 may be a UE. The apparatus 1002 includes a reception component 1004, an event component 1006, a detection component 1008, a random access component 1012, and a transmission component 1010.

The event component 1006 determines that a random access event has occurred. When the UE is in a connected state, the random access event includes at least one of: reception of a request from the base station to initiate a random access to the base station, a handover of the UE from a second base station to the base station, an up-link data arrival without up-link synchronization, a down-link data arrival without up-link synchronization, and a beam recovery request.

The reception component 1004 receives signals 1062 from a base station 1050 and sends the signals 1062 to the detection component 1008. The detection component 1008 detects one or more down-link reference signals that are UE-specifically configured or predefined. The random access component 1012 selects a first message that is associated with a first down-link reference signal of the one or more down-link reference signals. The first down-link reference signal is quasi-colocated with a first DMRS of a serving control channel of the UE. In certain configurations, the first message includes a preamble sequence. The first message is selected from a group of messages that are associated with the first down-link reference signal. In certain configurations, the first down-link reference signal is a channel state information reference signal or a synchronization signal block received. In certain configurations, the first down-link reference signal is directly quasi-colocated with the first DMRS. In certain configurations, the first down-link reference signal is quasi-colocated with the first DMRS through one or more intermediate signals.

The random access component 1012 sends the first message to the transmission component 1010, which in turn sends the first message to the base station 1050 to request a random access to the base station. In certain configurations, the random access event is the reception of the request. The reception component 1004 receives a second message from the base station in response to the first message. The reception component 1004 sends the second message to the random access component 1012. The random access component 1012 determines that a DMRS included in the request and a DMRS included in the second message are quasi-colocated. In certain configurations, the request is a PDCCH order. The second message includes a PDCCH command and a random access response. In certain configurations, the random access event is the beam failure recovery request. The PDCCH command is scrambled by a C-RNTI of the UE.

FIG. 11 is a diagram 1100 illustrating an example of a hardware implementation for an apparatus 1002′ employing a processing system 1114. The apparatus 1002′ may be a UE. The processing system 1114 may be implemented with a bus architecture, represented generally by a bus 1124. The bus 1124 may include any number of interconnecting buses and bridges depending on the specific application of the processing system 1114 and the overall design constraints. The bus 1124 links together various circuits including one or more processors and/or hardware components, represented by one or more processors 1104, the reception component 1004, the event component 1006, the detection component 1008, the transmission component 1010, the random access component 1012, and a computer-readable medium/memory 1106. The bus 1124 may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, etc.

The processing system 1114 may be coupled to a transceiver 1110, which may be one or more of the transceivers 254. The transceiver 1110 is coupled to one or more antennas 1120, which may be the communication antennas 252.

The transceiver 1110 provides a means for communicating with various other apparatus over a transmission medium. The transceiver 1110 receives a signal from the one or more antennas 1120, extracts information from the received signal, and provides the extracted information to the processing system 1114, specifically the reception component 1004. In addition, the transceiver 1110 receives information from the processing system 1114, specifically the transmission component 1010, and based on the received information, generates a signal to be applied to the one or more antennas 1120.

The processing system 1114 includes one or more processors 1104 coupled to a computer-readable medium/memory 1106. The one or more processors 1104 are responsible for general processing, including the execution of software stored on the computer-readable medium/memory 1106. The software, when executed by the one or more processors 1104, causes the processing system 1114 to perform the various functions described supra for any particular apparatus. The computer-readable medium/memory 1106 may also be used for storing data that is manipulated by the one or more processors 1104 when executing software. The processing system 1114 further includes at least one of the reception component 1004, the event component 1006, the detection component 1008, the transmission component 1010, and the random access component 1012. The components may be software components running in the one or more processors 1104, resident/stored in the computer readable medium/memory 1106, one or more hardware components coupled to the one or more processors 1104, or some combination thereof. The processing system 1114 may be a component of the UE 250 and may include the memory 260 and/or at least one of the TX processor 268, the RX processor 256, and the communication processor 259.

In one configuration, the apparatus 1002/apparatus 1002′ for wireless communication includes means for performing each of the operations of FIG. 8. The aforementioned means may be one or more of the aforementioned components of the apparatus 1002 and/or the processing system 1114 of the apparatus 1002′ configured to perform the functions recited by the aforementioned means.

As described supra, the processing system 1114 may include the TX Processor 268, the RX Processor 256, and the communication processor 259. As such, in one configuration, the aforementioned means may be the TX Processor 268, the RX Processor 256, and the communication processor 259 configured to perform the functions recited by the aforementioned means.

It is understood that the specific order or hierarchy of blocks in the processes/flowcharts disclosed is an illustration of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of blocks in the processes/flowcharts may be rearranged. Further, some blocks may be combined or omitted. The accompanying method claims present elements of the various blocks in a sample order, and are not meant to be limited to the specific order or hierarchy presented.

The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects. Unless specifically stated otherwise, the term “some” refers to one or more. Combinations such as “at least one of A, B, or C,” “one or more of A, B, or C,” “at least one of A, B, and C,” “one or more of A, B, and C,” and “A, B, C, or any combination thereof” include any combination of A, B, and/or C, and may include multiples of A, multiples of B, or multiples of C. Specifically, combinations such as “at least one of A, B, or C,” “one or more of A, B, or C,” “at least one of A, B, and C,” “one or more of A, B, and C,” and “A, B, C, or any combination thereof” may be A only, B only, C only, A and B, A and C, B and C, or A and B and C, where any such combinations may contain one or more member or members of A, B, or C. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. The words “module,” “mechanism,” “element,” “device,” and the like may not be a substitute for the word “means.” As such, no claim element is to be construed as a means plus function unless the element is expressly recited using the phrase “means for.” 

What is claimed is:
 1. A method of wireless communication of a user equipment (UE), comprising: receiving a first Demodulation Reference Signal (DMRS) on a serving control channel of the UE; determining that a random access event has occurred; receiving a plurality of down-link reference signals each being a Synchronization Signal Block (SSB) or a channel state information reference signal (CSI-RS); selecting a first down-link reference signal from the plurality of down-link reference signals, the first down-link reference signal being quasi-colocated with the first DMRS and UE-specifically configured or predefined; selecting a first message from a group of messages that each are associated with the first down-link reference signal; and sending the first message to a base station to request a random access to the base station.
 2. The method of claim 1, wherein the first message includes a preamble sequence, wherein the first message is selected from a group of messages that are associated with the first down-link reference signal.
 3. The method of claim 1, wherein the first down-link reference signal is a synchronization signal block.
 4. The method of claim 1, wherein the first down-link reference signal is directly quasi-colocated with the first DMRS.
 5. The method of claim 1, wherein the first down-link reference signal is quasi-colocated with the first DMRS through one or more intermediate signals.
 6. The method of claim 1, wherein, when the UE is in a connected state, the random access event includes at least one of: reception of a request from the base station to initiate a random access to the base station; a handover of the UE from a second base station to the base station; an up-link data arrival without up-link synchronization; a down-link data arrival without up-link synchronization; and a beam failure recovery request.
 7. The method of claim 6, further comprising: receiving a second message from the base station in response to the first message by assuming that a DMRS included in the request and a DMRS included in the second message are quasi-colocated.
 8. The method of claim 7, wherein the random access event is the reception of the request, wherein the request is a physical downlink control channel (PDCCH) order, wherein the second message includes a PDCCH command and a random access response.
 9. The method of claim 7, wherein the random access event is the beam failure recovery request, wherein the second message is scrambled by a cell radio network temporary identifier (C-RNTI) of the UE.
 10. An apparatus for wireless communication, the apparatus being a user equipment (UE), comprising: a memory; and at least one processor coupled to the memory and configured to: receive a first Demodulation Reference Signal (DMRS) on a serving control channel of the UE; determine that a random access event has occurred; receive a plurality of down-link reference signals each being a Synchronization Signal Block (SSB) or a channel state information reference signal (CSI-RS); select a first down-link reference signal from the plurality of down-link reference signals, the first down-link reference signal being quasi-colocated with the first DMRS and UE-specifically configured or predefined; select a first message from a group of messages that each are associated with the first down-link reference signal; and send the first message to a base station to request a random access to the base station.
 11. The apparatus of claim 10, wherein the first message includes a preamble sequence, wherein the first message is selected from a group of messages that are associated with the first down-link reference signal.
 12. The apparatus of claim 10, wherein the first down-link reference signal is a synchronization signal block.
 13. The apparatus of claim 10, wherein the first down-link reference signal is directly quasi-colocated with the first DMRS.
 14. The apparatus of claim 10, wherein the first down-link reference signal is quasi-colocated with the first DMRS through one or more intermediate signals.
 15. The apparatus of claim 10, wherein, when the UE is in a connected state, the random access event includes at least one of: reception of a request from the base station to initiate a random access to the base station; a handover of the UE from a second base station to the base station; an up-link data arrival without up-link synchronization; a down-link data arrival without up-link synchronization; and a beam failure recovery request.
 16. The apparatus of claim 15, wherein the at least one processor is further configured to: receive a second message from the base station in response to the first message by assuming that a DMRS included in the request and a DMRS included in the second message are quasi-colocated.
 17. The apparatus of claim 16, wherein the random access event is the reception of the request, wherein the request is a physical downlink control channel (PDCCH) order, wherein the second message includes a PDCCH command and a random access response.
 18. The apparatus of claim 16, wherein the random access event is the beam failure recovery request, wherein the second message is scrambled by a cell radio network temporary identifier (C-RNTI) of the UE.
 19. A non-transitory computer-readable medium storing computer executable code for wireless communication of wireless equipment, comprising code to: receive a first Demodulation Reference Signal (DMRS) on a serving control channel of the UE; determine that a random access event has occurred; receive a plurality of down-link reference signals each being a Synchronization Signal Block (SSB) or a channel state information reference signal (CSI-RS); select a first down-link reference signal from the plurality of down-link reference signals, the first down-link reference signal being quasi-colocated with the first DMRS and UE-specifically configured or predefined; select a first message from a group of messages that each are associated with the first down-link reference signal; and send the first message to a base station to request a random access to the base station.
 20. The non-transitory computer-readable medium of claim 19, wherein the first message includes a preamble sequence, wherein the first message is selected from a group of messages that are associated with the first down-link reference signal. 